SLIDE PROBLEMS PERSIST AT HIGHWAY 77 OVERPASS

CAPE GIRARDEAU -- Twenty-five years ago, the Missouri Highway and Transportation Department raised the highway over the St. Louis-Southwestern (Cotton Belt) Railroad on Highway 77, north of Chaffee.

The project was a success in that it stopped the grade crossing collisions. The same cannot be said for the overpass itself.

Almost since it was completed in the mid-1960s, the overpass has been plagued with earth slides on all four sides of the earthen approaches to the bridge.

During the summer months, the clay soil dries out, leaving large cracks on the surface of the slopes. When it rains, water pours into the cracks and deep into the soil, causing it to become unstable.

After the slides threatened the integrity of the highway and safety of motorists, plans were developed to solve the problem. In 1984 and 1986, the highway department spent nearly a half-million dollars on a repair project.

Highway department engineers thought they had found a solution to the problem by injecting a lime fly-ash slurry mixture into the slopes. As the lime dried and hardened, it was supposed to keep out moisture.

But District Ten Engineer Bob Sfreddo says it didn't work out that way.

"Where the lime was able to penetrate, the soil did remain stable, but unfortunately, the slurry mix was not able to penetrate throughout the soil," he explained last week. "Consequently, there was some remaining weakness and that has caused more earth slippages to occur on the approaches."

Sfreddo said the large number of heavy freight trains that rumble beneath the overpass at high speeds probably have not helped the problem.

The highway department will try again this year to resolve the problem. This time, Sfreddo is optimistic it can be done.

The state awarded a $857,431 contract last month to Robertson Inc. of Poplar Bluff to stabilize the fill slopes at each end of the overpass.

Sfreddo said the project should begin around the first of May, weather permitting, and barring any unforeseen delays, should be completed by the end of the 1991 construction season.

The work is being funded through money furnished by the road and bridge replacement improvement program previously approved by Missouri voters.

"We have studied the problem very closely," he said. "Our plan is to have the contractor remove some of the soil on the slopes by cutting back the angle of slopes from a two-to-one, to 1-to-one ratio. The material that is removed will be mechanically mixed with dry lime to make sure it is thoroughly mixed."

Sfreddo said while the slopes are cut back, drain pipes will be installed, and an 18-inch blanket of sand will be laid on top of the subsoil before the upper layer of clay mixed with lime is replaced.

"This top layer of lime and clay should make the soil impervious to water. What water does get through will drain into the sand layer and into the drain pipes," he explained. "We hope that will cure the pro~blem."

Sfreddo said when the overpass was constructed, engineers were not aware of the unstable characteristics of the clay soil when exposed to moisture and dry weather. "But we learned from that mistake," he said.

When the nearby Route N railroad overpass was built several years ago at Rockview, north of Chaffee, Sfreddo said soil from the hills east of Rockview was trucked in to the overpass site. So far, there have been no problems with the earthen approaches at the Route N overpass, Sfreddo noted.

Sfreddo said several other alternatives were considered at the Highway 77 overpass. "We talked about taking the whole thing (earth approaches) down and starting from the ground up, but that would have cost at least $2.4 million, and exposed highway traffic to the hazards of crossing the busy railroad track."

He said engineers also considered using large sheets of plastic Telar to lay on top of the slopes to keep out the moisture. That was rejected as being too expensive, as was the idea of using a rock dike.

"We also considered expanding the angle of the slope, but there is a drainage ditch and two large ponds located just west of the overpass, so we were really hemmed in as far as any additional right-of-way," he said.

Sfreddo said at least two other overpasses, one in New Madrid County and the other in Pemiscot County, were successfully treated with the lime fly-ash slurry mixture, with no additional slippage problems.

"The Highway 77 overpass has been our only major problem, and we hope this latest project will take care of the problem," Sfreddo said.